bitmap.h

   1 /*
   2  * bitmap.h: Copyright (C) Peter T. Breuer (ptb@ot.uc3m.es) 2003
   3  *
   4  * additions: Copyright (C) 2003-2004, Paul Clements, SteelEye Technology, Inc.
   5  */
   6 #ifndef BITMAP_H
   7 #define BITMAP_H 1
   8
   9 #define BITMAP_MAJOR 3
  10 #define BITMAP_MINOR 38
  11
  12 /*
  13  * in-memory bitmap:
  14  *
  15  * Use 16 bit block counters to track pending writes to each "chunk".
  16  * The 2 high order bits are special-purpose, the first is a flag indicating
  17  * whether a resync is needed.  The second is a flag indicating whether a
  18  * resync is active.
  19  * This means that the counter is actually 14 bits:
  20  *
  21  * +--------+--------+------------------------------------------------+
  22  * | resync | resync |               counter                          |
  23  * | needed | active |                                                |
  24  * |  (0-1) |  (0-1) |              (0-16383)                         |
  25  * +--------+--------+------------------------------------------------+
  26  *
  27  * The "resync needed" bit is set when:
  28  *    a '1' bit is read from storage at startup.
  29  *    a write request fails on some drives
  30  *    a resync is aborted on a chunk with 'resync active' set
  31  * It is cleared (and resync-active set) when a resync starts across all drives
  32  * of the chunk.
  33  *
  34  *
  35  * The "resync active" bit is set when:
  36  *    a resync is started on all drives, and resync_needed is set.
  37  *       resync_needed will be cleared (as long as resync_active wasn't already set).
  38  * It is cleared when a resync completes.
  39  *
  40  * The counter counts pending write requests, plus the on-disk bit.
  41  * When the counter is '1' and the resync bits are clear, the on-disk
  42  * bit can be cleared aswell, thus setting the counter to 0.
  43  * When we set a bit, or in the counter (to start a write), if the fields is
  44  * 0, we first set the disk bit and set the counter to 1.
  45  *
  46  * Also, we'll hijack the "map" pointer itself and use it as two 16 bit block
  47  * counters as a fallback when "page" memory cannot be allocated:
  48  *
  49  * Normal case (page memory allocated):
  50  *
  51  *     page pointer (32-bit)
  52  *
  53  *     [ ] ------+
  54  *               |
  55  *               +-------> [   ][   ]..[   ] (4096 byte page == 2048 counters)
  56  *                          c1   c2    c2048
  57  *
  58  * Hijacked case (page memory allocation failed):
  59  *
  60  *     hijacked page pointer (32-bit)
  61  *
  62  *     [                  ][              ] (no page memory allocated)
  63  *      counter #1 (16-bit) counter #2 (16-bit)
  64  *
  65  */
  66
  67 #ifdef __KERNEL__
  68
  69 #define PAGE_BITS (PAGE_SIZE << 3)
  70 #define PAGE_BIT_SHIFT (PAGE_SHIFT + 3)
  71
  72 typedef __u16 bitmap_counter_t;
  73 #define COUNTER_BITS 16
  74 #define COUNTER_BIT_SHIFT 4
  75 #define COUNTER_BYTE_RATIO (COUNTER_BITS / 8)
  76 #define COUNTER_BYTE_SHIFT (COUNTER_BIT_SHIFT - 3)
  77
  78 #define NEEDED_MASK ((bitmap_counter_t) (1 << (COUNTER_BITS - 1)))
  79 #define RESYNC_MASK ((bitmap_counter_t) (1 << (COUNTER_BITS - 2)))
  80 #define COUNTER_MAX ((bitmap_counter_t) RESYNC_MASK - 1)
  81 #define NEEDED(x) (((bitmap_counter_t) x) & NEEDED_MASK)
  82 #define RESYNC(x) (((bitmap_counter_t) x) & RESYNC_MASK)
  83 #define COUNTER(x) (((bitmap_counter_t) x) & COUNTER_MAX)
  84
  85 /* how many counters per page? */
  86 #define PAGE_COUNTER_RATIO (PAGE_BITS / COUNTER_BITS)
  87 /* same, except a shift value for more efficient bitops */
  88 #define PAGE_COUNTER_SHIFT (PAGE_BIT_SHIFT - COUNTER_BIT_SHIFT)
  89 /* same, except a mask value for more efficient bitops */
  90 #define PAGE_COUNTER_MASK  (PAGE_COUNTER_RATIO - 1)
  91
  92 #define BITMAP_BLOCK_SIZE 512
  93 #define BITMAP_BLOCK_SHIFT 9
  94
  95 /* how many blocks per chunk? (this is variable) */
  96 #define CHUNK_BLOCK_RATIO(bitmap) ((bitmap)->chunksize >> BITMAP_BLOCK_SHIFT)
  97 #define CHUNK_BLOCK_SHIFT(bitmap) ((bitmap)->chunkshift - BITMAP_BLOCK_SHIFT)
  98 #define CHUNK_BLOCK_MASK(bitmap) (CHUNK_BLOCK_RATIO(bitmap) - 1)
  99
 100 /* when hijacked, the counters and bits represent even larger "chunks" */
 101 /* there will be 1024 chunks represented by each counter in the page pointers */
 102 #define PAGEPTR_BLOCK_RATIO(bitmap) \
 103                         (CHUNK_BLOCK_RATIO(bitmap) << PAGE_COUNTER_SHIFT >> 1)
 104 #define PAGEPTR_BLOCK_SHIFT(bitmap) \
 105                         (CHUNK_BLOCK_SHIFT(bitmap) + PAGE_COUNTER_SHIFT - 1)
 106 #define PAGEPTR_BLOCK_MASK(bitmap) (PAGEPTR_BLOCK_RATIO(bitmap) - 1)
 107
 108 /*
 109  * on-disk bitmap:
 110  *
 111  * Use one bit per "chunk" (block set). We do the disk I/O on the bitmap
 112  * file a page at a time. There's a superblock at the start of the file.
 113  */
 114
 115 /* map chunks (bits) to file pages - offset by the size of the superblock */
 116 #define CHUNK_BIT_OFFSET(chunk) ((chunk) + (sizeof(bitmap_super_t) << 3))
 117
 118 #endif
 119
 120 /*
 121  * bitmap structures:
 122  */
 123
 124 #define BITMAP_MAGIC 0x6d746962
 125
 126 /* use these for bitmap->flags and bitmap->sb->state bit-fields */
 127 enum bitmap_state {
 128         BITMAP_ACTIVE = 0x001, /* the bitmap is in use */
 129         BITMAP_STALE  = 0x002  /* the bitmap file is out of date or had -EIO */
 130 };
 131
 132 /* the superblock at the front of the bitmap file -- little endian */
 133 typedef struct bitmap_super_s {
 134         __u32 magic;        /*  0  BITMAP_MAGIC */
 135         __u32 version;      /*  4  the bitmap major for now, could change... */
 136         __u8  uuid[16];     /*  8  128 bit uuid - must match md device uuid */
 137         __u64 events;       /* 24  event counter for the bitmap (1)*/
 138         __u64 events_cleared;/*32  event counter when last bit cleared (2) */
 139         __u64 sync_size;    /* 40  the size of the md device's sync range(3) */
 140         __u32 state;        /* 48  bitmap state information */
 141         __u32 chunksize;    /* 52  the bitmap chunk size in bytes */
 142         __u32 daemon_sleep; /* 56  seconds between disk flushes */
 143
 144         __u8  pad[256 - 60]; /* set to zero */
 145 } bitmap_super_t;
 146
 147 /* notes:
 148  * (1) This event counter is updated before the eventcounter in the md superblock
 149  *    When a bitmap is loaded, it is only accepted if this event counter is equal
 150  *    to, or one greater than, the event counter in the superblock.
 151  * (2) This event counter is updated when the other one is *if*and*only*if* the
 152  *    array is not degraded.  As bits are not cleared when the array is degraded,
 153  *    this represents the last time that any bits were cleared.
 154  *    If a device is being added that has an event count with this value or
 155  *    higher, it is accepted as conforming to the bitmap.
 156  * (3)This is the number of sectors represented by the bitmap, and is the range that
 157  *    resync happens across.  For raid1 and raid5/6 it is the size of individual
 158  *    devices.  For raid10 it is the size of the array.
 159  */
 160
 161 #ifdef __KERNEL__
 162
 163 /* the in-memory bitmap is represented by bitmap_pages */
 164 struct bitmap_page {
 165         /*
 166          * map points to the actual memory page
 167          */
 168         char *map;
 169         /*
 170          * in emergencies (when map cannot be alloced), hijack the map
 171          * pointer and use it as two counters itself
 172          */
 173         unsigned int hijacked;
 174         /*
 175          * count of dirty bits on the page
 176          */
 177         int count;
 178 };
 179
 180 /* keep track of bitmap file pages that have pending writes on them */
 181 struct page_list {
 182         struct list_head list;
 183         struct page *page;
 184 };
 185
 186 /* the main bitmap structure - one per mddev */
 187 struct bitmap {
 188         struct bitmap_page *bp;
 189         unsigned long pages; /* total number of pages in the bitmap */
 190         unsigned long missing_pages; /* number of pages not yet allocated */
 191
 192         mddev_t *mddev; /* the md device that the bitmap is for */
 193
 194         int counter_bits; /* how many bits per block counter */
 195
 196         /* bitmap chunksize -- how much data does each bit represent? */
 197         unsigned long chunksize;
 198         unsigned long chunkshift; /* chunksize = 2^chunkshift (for bitops) */
 199         unsigned long chunks; /* total number of data chunks for the array */
 200
 201         /* We hold a count on the chunk currently being synced, and drop
 202          * it when the last block is started.  If the resync is aborted
 203          * midway, we need to be able to drop that count, so we remember
 204          * the counted chunk..
 205          */
 206         unsigned long syncchunk;
 207
 208         __u64   events_cleared;
 209
 210         /* bitmap spinlock */
 211         spinlock_t lock;
 212
 213         struct file *file; /* backing disk file */
 214         struct page *sb_page; /* cached copy of the bitmap file superblock */
 215         struct page **filemap; /* list of cache pages for the file */
 216         unsigned long *filemap_attr; /* attributes associated w/ filemap pages */
 217         unsigned long file_pages; /* number of pages in the file */
 218
 219         unsigned long flags;
 220
 221         /*
 222          * the bitmap daemon - periodically wakes up and sweeps the bitmap
 223          * file, cleaning up bits and flushing out pages to disk as necessary
 224          */
 225         mdk_thread_t *daemon;
 226         unsigned long daemon_sleep; /* how many seconds between updates? */
 227
 228         /*
 229          * bitmap write daemon - this daemon performs writes to the bitmap file
 230          * this thread is only needed because of a limitation in ext3 (jbd)
 231          * that does not allow a task to have two journal transactions ongoing
 232          * simultaneously (even if the transactions are for two different
 233          * filesystems) -- in the case of bitmap, that would be the filesystem
 234          * that the bitmap file resides on and the filesystem that is mounted
 235          * on the md device -- see current->journal_info in jbd/transaction.c
 236          */
 237         mdk_thread_t *write_daemon;
 238         mdk_thread_t *writeback_daemon;
 239         spinlock_t write_lock;
 240         struct semaphore write_ready;
 241         struct semaphore write_done;
 242         unsigned long writes_pending;
 243         wait_queue_head_t write_wait;
 244         struct list_head write_pages;
 245         struct list_head complete_pages;
 246         mempool_t *write_pool;
 247 };
 248
 249 /* the bitmap API */
 250
 251 /* these are used only by md/bitmap */
 252 int  bitmap_create(mddev_t *mddev);
 253 void bitmap_destroy(mddev_t *mddev);
 254 int  bitmap_active(struct bitmap *bitmap);
 255
 256 char *file_path(struct file *file, char *buf, int count);
 257 void bitmap_print_sb(struct bitmap *bitmap);
 258 int bitmap_update_sb(struct bitmap *bitmap);
 259
 260 int  bitmap_setallbits(struct bitmap *bitmap);
 261
 262 /* these are exported */
 263 void bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors);
 264 void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors,
 265                      int success);
 266 int bitmap_start_sync(struct bitmap *bitmap, sector_t offset, int *blocks);
 267 void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, int *blocks, int aborted);
 268 void bitmap_close_sync(struct bitmap *bitmap);
 269
 270 int bitmap_unplug(struct bitmap *bitmap);
 271 #endif
 272
 273 #endif